The use of Petri dishes for growing colonies of microorganisms such as bacteria or fungi is well known. A Petri dish typically comprises a short cylindrical open dish for holding microorganism growth medium and an overlapping cylindrical cover that isolates the growth medium and microorganisms from the external environment. Petri dish covers may be loosely fitting so that the seal and the dish arises simply from the weight of the cover bearing upon the cylindrical side walls of the dish. Petri dish covers may also be tightly securable to and detachable from the dish, which facilitates lifting the Petri dish by its cover.
One such design is disclosed in U.S. Pat. No. 3,769,936, wherein the cover may be secured to the dish by ribs in the side walls of the cover that resiliently contact the side walls of the dish so as to form a compression fit. However, this design has the inherent drawback that the compression fit is often either too tight to allow ready disengagement between the cover and dish or too loose, which can lead to accidental spillage or contamination when handling the Petri dish.
What is needed therefore is a lockable Petri dish that does not lock except upon application of a specific intentionally applied force, that provides a secure locking engagement between the cover and the dish, and which may be readily disengaged from the locking engagement. These needs are met by the present invention, which is summarized and described in detail below.